What investigations can help students best understand conservation of matter? The Investigating Matter tasks are intended to elicit preservice teachers’ CKT related to the conservation of matter. The open-ended task asks preservice teachers to identify an investigation that would provide students with evidence to support this idea, while the multiple-choice version, Selecting Investigation of Matter, provides them several alternatives to consider. The packet contains tasks, an elaborated answer key, lesson plans, reading pages, and other resources to support preservice teachers in selecting appropriate investigations and demonstrations to help students understand the conservation of matter.